1. Field of the Invention
The present invention involves coated proppant slurries and using such slurries in subterranean applications such as production enhancement and sand control. More particularly, the present invention relates to stable resin-coated proppant suspensions that need not be immediately used once they are formed.
2. Description of Related Art
Servicing fluids comprising particulates are used in a variety of operations performed on subterranean wells, such as production stimulation operations like fracturing and well completion operations like gravel packing. Often, it is desirable for such particulates to consolidate into a permeable pack or mass. One method of achieving such consolidation involves coating the particulates with a curable resin before they are used in a subterranean operation so that they consolidate once down hole.
One example of a production stimulation operation using a servicing fluid having particulates suspended therein is hydraulic fracturing, wherein a formation is treated to increase its permeability by hydraulically fracturing the formation to create or enhance one or more cracks or “fractures.” Such hydraulic fracturing is usually accomplished by injecting a viscous fracturing fluid into the subterranean formation at a rate and pressure sufficient to cause the formation to break down and produce one or more fractures or enhance one or more natural fractures. The fracture or fractures may be horizontal or vertical, with the latter usually predominating, and with the tendency toward vertical fractures increasing with the depth of the formation being fractured. The fracturing fluid is generally a highly viscous gel, emulsion, or foam that comprises a particulate material often referred to as proppant. In some fracturing operations, commonly known as “water fracturing” operations, the fracturing fluid viscosity is somewhat lowered, the proppant concentration is in the range of from about 0.5 to about 2 pounds per gallon, and the proppant remains in suspension because the fracturing fluid is injected into the formation at a substantially higher velocity. Whether a highly viscous fluid or a less viscous fluid with a higher velocity is used, proppant is deposited in the fracture and functions, inter alia, to hold the fracture open while maintaining channels through which produced fluids can flow upon completion of the fracturing treatment and release of the attendant hydraulic pressure.
An example of a well completion operation using a treating fluid containing particulates is gravel packing. Gravel packing treatments are used, inter alia, to reduce the migration of unconsolidated formation particulates into the well bore. In gravel packing operations, particles known in the art as gravel are carried to a well bore by a hydrocarbon or water carrier fluid. That is, the particulates are suspended in a carrier fluid, which may be viscosified, and the carrier fluid is pumped into a well bore in which the gravel pack is to be placed. The carrier fluid leaks off into the subterranean zone and/or is returned to the surface while the particulates are left in the zone. The resultant gravel pack acts as a filter to separate formation sands from produced fluids while permitting the produced fluids to flow into and through the well bore. Typically, gravel pack operations involve placing a gravel pack screen in the well bore and packing the surrounding annulus between the screen and the well bore with gravel designed to prevent the passage of formation sands through the pack. The gravel pack screen is generally a filter assembly used to support and retain the gravel placed during the gravel pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of a well bore, the production fluid, and the subterranean formation sands. When installing the gravel pack, the gravel is carried to the formation in the form of a slurry by mixing the gravel with a viscosified carrier fluid. Once the gravel is placed in the well bore, the viscosity of the carrier fluid is reduced and it is returned to the surface. Such gravel packs are used to stabilize the formation while causing minimal impairment to well productivity. The gravel, inter alia, acts to prevent formation sands from occluding the screen or migrating with the produced fluids, and the screen, inter alia, acts to prevent the gravel from entering the well bore.
In some situations the processes of hydraulic fracturing and gravel packing are combined into a single treatment to provide a stimulated production and an annular gravel pack to reduce formation sand production. Such treatments are often referred to as “frac pack” operations. In some cases the treatments are completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation the hydraulic fracturing treatment ends in a screen out condition creating an annular gravel pack between the screen and casing. This allows both the hydraulic fracturing treatment and gravel pack to be placed in a single operation. In other cases the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
In order to prevent the subsequent flowback of proppant, gravel or other unconsolidated particulates with the produced fluids, a portion of the particulate introduced into the fractures or gravel packs may be coated with a hardenable resin composition. In the case of a fracturing operation, the fracture then closes on the proppant and applies pressure on the resin-coated particulates, causing the particles to be forced into contact with each other while the resin composition hardens. The hardening of the resin composition under pressure brings about the consolidation of the resin-coated proppant particles into a hard permeable mass having compressive and tensile strength meant to prevent unconsolidated particulates and formation sand from flowing out of the fractures with produced fluids. Flowback of formation sand with produced fluids is undesirable as it may erode metal equipment, plug piping and vessels, cause damage to valves, instruments, and other production equipment, and ultimately reduce the potential production of the well.